The present invention relates to an image processing device for use in a copier, printer or similar image forming apparatus and, more particularly, to an image processing device for processing an image read by an image scanner or similar image reading device.
The problem with a copier, printer or similar image forming apparatus with an image scanner is that when the scanner scans a spread book document, the bound portion of the book rises above a glass platen, i.e., away from the focal plane of the scanner. As a result, the image of the bound portion is distorted, shadowed, blurred or otherwise deteriorated, as well known in the art. This is particularly true with a relatively thick book document. The operator therefore must press the bound portion of the spread book document against the glass platen, sometimes damaging the bound portion. When the spread book document is read by a flat bed type scanner customarily with a copier, the image of the bound portion of the document is distorted, shadowed, blurred or otherwise deteriorated.
Japanese Patent Laid-Open Publication No. 60-65668 teaches an image processing device capable of reproducing a distortion-free image. The device taught in this document measures the length of a spread book in the subscanning direction, determines the radius of curvature of the bound portion of the book, and then executes processing with a deformed image. Japanese Patent Laid-Open Publication No. 60-65669 proposes an image processing device capable of correcting the deformation of an image by determining, based on the radius of curvature of the bound portion of a spread book, a correction value in the main scanning direction, and correcting information representative of the bound portion with the correction value. These conventional devices both include means for correcting the distortion of the portion of a read image representative of the bound portion in the main and subscanning directions. In any case, the configuration of the bound portion is determined in terms of a radius r on the basis of the length of the document and the actual length.
Japanese Patent Laid-Open Publication No. 58-130361 discloses an image reading device using a light-sensitive unit for reading the surface of a book or similar object having a substantial thickness. The distance between the light-sensitive unit and the object is measured in order to control the distance between the object and the light-sensitive unit or a lens. Japanese Patent Laid-Open Publication Nos. 61-171272, 61-237569 and 1-232872 teach a scanner and a reading device each including means for measuring the height of a document. This kind of scanner or reading device controls a relative speed between an image sensor and a document in accordance with the variation of the height of the document, thereby correcting the distortion of image data. These implementations each includes an extra sensor for measuring the distance to the surface of a document and moves it along the document.
Japanese Patent Laid-Open Publication No. 5-161000 proposes an image processing device including range finding means for determining distances to a plurality of points of a document, interpolating means for interpolating data representative of a document, and means for correcting the curvature of the book in response to the output of the interpolating means. Japanese Patent Laid-Open Publication No. 5-161001 discloses an image processing device including measuring means for measuring the configuration of a document, means for calculating an image extension rate pixel by pixel, and extending means for interpolating density to thereby extend pixels.
Japanese Patent Laid-Open Publication No. 5-161002 proposes an image processing device including measuring means for measuring the configuration of a document and means for correcting a curvature in the direction of lines (main scanning direction). This device corrects a curvature, corrects blurring, and then executes extension (subscanning direction). Japanese Patent Laid-Open Publication No. 5-161003 teaches an image processing device including boundary detecting means for detecting a boundary between a document and a glass platen, output detecting means for detecting an output at a point spaced from the boundary by a preselected distance, and means for correcting an output read.
Japanese Patent Laid-Open Publication No. 5-161004 discloses an image processing device including reading means for reading a document at a preselected distance from a glass platen, boundary detecting means for detecting a boundary between the document and the glass platen, height detecting means for determining the height of the document in response to the output of the boundary detecting means, and correcting means for executing correction in accordance with the output of the height detecting means. Japanese Patent Laid-Open Publication No. 6-164852 shows and describes an image processing device constructed to detect a boundary between a document and a glass platen, calculate a magnification change ratio (main scanning direction), and thereby correct the distortion of an image.
The above Laid-Open Publication Nos. 5-161003 and 5-161004, among others, each teaches an implementation for detecting a boundary between a document and a glass platen and thereby determining the height of the document so as to correct an image. Laid-Open Publication Nos. 5-16000, 5-161001, 1-161002, 5-161003, 5-161004 and 6-164852 deal with a spread book positioned face up.
The conventional image processing devices described above each includes means for correcting the portion of an image representative of the bound portion of a spread book in the main and subscanning directions. The correcting means translates the configuration of the bound portion to a radius r and determines the radius r on the basis of the length of the document and the actual length. This, however, brings about a problem that the distortion of the bound portion cannot be accurately corrected unless the bound portion is circular.
Laid-Open Publication Nos. 58-130361, 61-171272, 6-1237569 and 1-232872 each has a drawback that an extra sensor must be used and moved along a document in order to measure the distance to the document.
Further, Laid-Open Publication Nos. 5-161000, 5-161001, 5-161002, 5-161003, 5-161004 and 6-164852 dealing with a spread document positioned face up have the following problems. Because the spread book positioned face up is curved over its entire surface, it is necessary to measure the height of the entire spread pages by the detection of a boundary, and then execute correction over the entire curved pages. Moreover, none of the above documents teaches a specific method for the detection of a page boundary.